1. Field of the Invention
The present invention relates to an image processing method which prevents deterioration of a thermoreversible recording medium by reducing the damages due to repetitive recording and erasing of images, and an image processing device suitably which can be suitably used for the image processing method.
2. Description of the Related Art
As a method for recording and erasing an image onto and from a thermoreversible recording medium (hereinafter otherwise referred to as “reversible thermosensitive recording medium”, “recording medium” or “medium”) from a distance or when depressions and protrusions are created on the surface of the thermoreversible recording medium, there has been proposed a method using a noncontact laser (refer to Japanese Patent Application Laid-Open (JP-A) No. 2000-136022). This proposal discloses that image recording is carried out using a laser and image erasing is carried out using hot air, warm water, an infrared heater or the like.
Moreover, Japanese Patent (JP-B) No. 3350836 discloses that by controlling at least one of the irradiation time, the irradiation luminosity, the focus and the intensity distribution, it is possible to control the heating temperature in a manner that is divided into a first specific temperature and a second specific temperature of the thermoreversible recording medium, and by changing the cooling rate after heating, it is possible to form and erase an image on the whole surface or partially.
JP-B No. 3446316 describes use of two laser beams and the following methods: a method in which erasure is carried out with one laser beam being used as an elliptical or oval laser beam, and recording is carried out with the other laser beam being used as a circular laser beam; a method in which recording is carried out with the two laser beams being used in combination; and a method in which recording is carried out, with each of the two laser beams being modified and then these modified laser beams being used in combination. According to these methods, use of the two laser beams makes it possible to realize higher density image recording than use of one laser beam does.
Moreover, JP-A No. 2003-246144 proposes the method for realizing an image recording with high durability on a thermoreversible recording medium, in which an image of clear contrast can be recorded by erasing with laser light the energy and irradiation time of which are controlled to be 25% to 65% of the laser light used at the time of recording.
According to the conventional methods mentioned above, image recording and erasing can be carried out repeatedly using laser. However, as laser is not controlled, there is a problem such that a thermal damage is occurred locally on the area where lines are overlapped at the time of image recording.
In this connection, for example, JP-A No. 2003-127446 proposes to prevent the deterioration of a thermoreversible recording medium by lowering the energy at a certain interval at the time a straight line is recorded so as to reduce a local thermal damage. Moreover, JP-A No. 2007-69605 discloses that energy is uniformly applied to a thermoreversible recording medium by controlling the light intensity at the center portion to the same degree or less of the that in the peripheric portion in the light intensity distribution on the cross section in the substantially orthogonal direction with respect to the traveling direction of laser light, and thus deterioration of the thermoreversible recording medium is reduced even when image recording and erasing are repeated.
Moreover, Japanese Patent No. 3682295 and JP-A No. 2006-126851 proposes an image recording device which enables to irradiate a large area of a thermoreversible recording medium using a galvanometer mirror as a light scanning unit, and a fθ lens as a light condensing unit. However, in this proposal, aberrations are caused because the galvanometer mirror and the fθ lens are used, and a thermoreversible recording medium is deteriorated if image recording and erasing are repeatedly carried out with changing the scanning linear speed.
To solve the aforementioned problems, for example JP-A No. 2008-68630 discloses a method in which the light intensity distribution of laser light transmitting through the center portion of a fθ lens and traveling onto a thermoreversible recording medium is controlled so that excessive energy is not applied on the thermoreversible recording medium, even when the scanning linear speed is changed with the combination of an optical system using a galvanometer mirror and the fθ lens, and an optical lens as a light intensity distribution controlling unit for controlling the light intensity of laser light. According to this proposal, even when image recording and erasing are repeated with laser, the laser light transmitting through the center part of the fθ lens and traveling on the thermoreversible recording medium is not easily cause the deterioration of the thermoreversible recording medium.
However, according to the technique disclosed in JP-A No. 2008-68630, the light intensity distribution of the laser light passing through the peripheric portion of the fθ lens and traveling onto the thermoreversible recording medium becomes sharp in its shape compared to that of the laser light passing through the center portion of the fθ lens and traveling onto the thermoreversible recording medium, and as a result, the laser light partially having large intensity compared to the laser light passing through the center portion of the fθ lens and traveling to the thermoreversible recording medium is transmitted through the peripheric portion of the fθ lens and delivered to the thermoreversible recording medium. If image recording and erasing are repetitively performed in this condition, the thermoreversible recording medium will be deteriorated at an early stage.
Accordingly, there is currently no image processing method and no image processing device which suppress the deterioration of a thermoreversible recording medium when image recording and erasing are repeatedly performed, without applying excessive energy to the thermoreversible recording medium from laser light passing through a center portion of a fθ lens and traveling onto the thermoreversible recording medium, and laser light passing through a peripheric portion of the fθ lens and traveling onto the thermoreversible recording medium, and also are capable of uniformly recording an image. For this reason, it is a situation that such image processing method and image processing device are desired.